A. Field of the Invention
This invention relates to the field of art of on-line gas measurement and analysis systems and particularly with respect to gas chromatograph systems.
B. Background Art
It has become increasingly important, particularly over the last several years, to quantitatively measure the amount of natural gas being transmitted through a pipeline. This requirement has been based on the heating value or calorific content of the natural gas traveling through the pipeline when it has been sold or otherwise transferred. All of those involved in the sale, purchase and transmission of the natural gas now recognize the need for the highest possible accuracy in both energy content and flow measurement.
In the past some approaches to energy measurement have been taken, generally based on indirect measurement techniques with energy content manually integrated with flow data. Such indirect measurement generally consisted of estimates and assumptions of many physical parameters found in both flow and energy equations. Each of these techniques has relied on assumptions that a given operating parameter or set of parameters remains constant over some period i.e. pressure, temperature, supercompressibility and others. By definition, each of these assumptions introduces inaccuracies in energy measurement. Economic pressures result from the rapid escalation of the cost of fuel gas. As the cost of gas increases, the marginal cost increases. Specifically, present methods of measurement permit too great a margin of error, as the cost of the fuel unaccounted for becomes significant due to the price increases per unit of fuel. In this same light, both purchasers and suppliers of fuel gas have been utilizing contracts which specify a price per "Dekatherm", a unit of energy content, rather than simply cost per volume, (dollars per cubic feet, for example). Economic pressure and increased use of "Dekatherm" contracts have combined to dictate the use of more accurate total energy measurement for fuel gas.